Cannot stat/ no such file or directory

I think ive made some mistakes that I dont have the knowledge or time to recover, so I have found a good video to build from source and am currently working on that. Thank you for the help, but due to me I'm starting from square one.

Is there anything special you need to use that would require building from sources and patching?
For normal stuff, it is as easy as downloading the latest ISO file, installing it, then in a terminal type
sudo apt update
sudo apt install linuxcnc
That should also install the RTAI kernel together with the RTAI version of LinuxCNC, although i have never tested it.

I never tried that mainly because I did not know "linuxcnc" had the RTAI kernal and the "linuxcnc-uspace" was the PREEMPT rt.